Providing a description of aircraft intent

ABSTRACT

The present disclosure provides a computer-implemented method of generating a description of aircraft intent expressed in a formal language that provides an unambiguous description of an aircraft&#39;s intended motion and configuration during a period of flight. A description of flight intent is parsed to provide instances of flight intent, each instance of flight intent spanning a flight segment. For each flight segment, an associated flight segment description is generated that comprises one or more instances of flight intent that describe the aircraft&#39;s motion in at least one degree of freedom of motion. One or more instances of flight intent are added to flight segments to close all degrees of freedom of motion. The flight segment descriptions are collated thereby providing a description of aircraft intent for the period of flight expressed in a formal language.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is related to and incorporates herein by reference inits entirety, co-pending U.S. patent application Ser. No. 13/901,603,concurrently filed and entitled “Providing a Description of AircraftIntent” which claims priority to EP Patent Application No. 12382194.4,filed on May 24, 2012 in the Spanish Patent Office.

This application is related to and incorporates herein by reference inits entirety, co-pending U.S. patent application Ser. No. 13/901,606,concurrently filed and entitled “Providing a Description of AircraftIntent” which claims priority to EP Patent Application No. 12382196.9,filed on May 24, 2012 in the Spanish Patent Office.

PRIORITY STATEMENT

This application claims the benefit of EP Patent Application No.12382195.1, filed on May 24, 2012 in the Spanish Patent Office, thedisclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present disclosure relates to providing a method of forming adescription of aircraft intent expressed using a formal language. Such adescription allows the path of an aircraft to be predictedunambiguously.

BACKGROUND

The ability to predict an aircraft's trajectory is useful for severalreasons. By trajectory, a four-dimensional description of the aircraft'spath is meant. The description may be the evolution of the aircraft'sstate with time, where the state may include the position of theaircraft's centre of mass and other aspects of its motion such asvelocity, attitude and weight.

For example, air traffic management (ATM) would benefit from an improvedability to predict an aircraft's four-dimensional trajectory. Airtraffic management is responsible for the safe separation of aircraft, aparticularly demanding task in congested airspace such as aroundairports. ATM decision-support tools based on accurate four-dimensionaltrajectory predictions could allow a greater volume of aircraft to behandled while maintaining safety.

The ability to predict an aircraft's four-dimensional trajectory willalso be of benefit to the management of autonomous vehicles such asunmanned air vehicles (UAVs), for example in programming flight plansfor UAVs as well as in commanding and de-conflicting their trajectories.

In order to predict an aircraft's four-dimensional trajectoryunambiguously, one must solve a set of differential equations that modelboth aircraft behaviour and atmospheric conditions. Different sets ofdifferential equations are available for use, some treating the aircraftas a six degrees of freedom of movement system and others treating theaircraft as a point mass with three degrees of freedom of movement. Inaddition, to solve the equations of motion, information concerning theaircraft's configuration is required as it will respond differently tocontrol commands depending upon its configuration. Hence, furtherdegrees of freedom of configuration may require definition that describethe configuration of the aircraft. For example, three degrees of freedomof configuration may be used to define landing gear configuration, speedbrake configuration and lift devices configuration. Accordingly,aircraft intent may need to close six degrees of freedom to define anunambiguous trajectory, three degrees corresponding to motion of theaircraft in three axes and the other three degrees corresponding toaircraft configuration.

The computation process requires inputs corresponding to the aircraftintent, for example a description of aircraft intent expressed using aformal language. The aircraft intent provides enough information topredict unambiguously the trajectory that will be flown by the aircraft.The aircraft intent is usually derived from a description of flightintent, that is more-basic information that does not allow anunambiguous determination of aircraft trajectory. Aircraft intent maycomprise information that captures basic commands, guidance modes andcontrol inputs at the disposal of the pilot and/or the flight managementsystem.

Aircraft intent must be distinguished from flight intent. Flight intentmay be thought of as a generalisation of the concept of a flight plan,and so will reflect operational constraints and objectives such as anintended or required route and operator preferences. Generally, flightintent will not unambiguously define an aircraft's trajectory, as it islikely to contain only some of the information necessary to close alldegrees of freedom. Put another way, there are likely to be manyaircraft trajectories that could be calculated that would satisfy agiven flight intent. Thus, flight intent may be regarded as a basicblueprint for a flight, but that lacks the specific details required tocompute unambiguously a trajectory. Thus additional information must becombined with the flight intent to derive the aircraft intent that doesallow an unambiguous prediction of the four-dimensional trajectory to beflown.

Aircraft intent is expressed using a set of parameters presented so asto allow equations of motion to be solved. The parameters may be leftopen (e.g. specifying a range of allowable parameters) or may bespecified as a particular value. The former is referred to as aninstance of parametric aircraft intent to distinguish it from the latterthat is referred to as complete aircraft intent or just as aircraftintent. The theory of formal languages may be used to implement thisformulation: an aircraft intent description language provides the set ofinstructions and the rules that govern the allowable combinations thatexpress the aircraft intent, and so allow a prediction of the aircrafttrajectory.

Co-pending U.S. patent application Ser. No. 12/679,275 published as US2010-0305781 A1, also in the name of The Boeing Company, describesaircraft intent in more detail, and the disclosure of this applicationis incorporated herein in its entirety by reference. Co-pending U.S.patent application Ser. No. 13/360,318 published as US 2012-0290154 A1,also in the name of The Boeing Company, describes flight intent in moredetail, and the disclosure of this application is incorporated herein inits entirety by reference.

SUMMARY

Against this background and according to a first aspect, the presentdisclosure resides in a computer-implemented method of generating adescription of aircraft intent expressed in a formal language thatprovides an unambiguous description of an aircraft's intended motion andconfiguration during a period of flight. The period of flight may be allor part of a flight from takeoff to landing, and may also includetaxiing on the ground.

The method comprises obtaining a description of flight intentcorresponding to a flight plan spanning the period of flight. Thisflight intent may be generated by a pilot or automatically generated byflight management software in the aircraft.

The method further comprises ensuring that the flight intent descriptionis parsed to provide instances of flight intent, each instance of flightintent spanning a flight segment with the flight segments togetherspanning the period of flight. Thus the flight intent descriptionscontained in the flight intent are reviewed and used to define flightsegments that correspond to the time intervals for which the flightintent description is active. Thus, the period of flight is divided intoa series of flight segments with the boundaries between flight segmentscorresponding to a flight intent description becoming active orexpiring. The descriptions of flight intent are generally referred toherein as instances of flight intent and the period of time for whichthey are active is generally referred to herein as their executioninterval. Ensuring that the parsing has been done may correspond tochecking that the received description of flight intent has been parsedin this way, or it may correspond to performing the parsing.

For each flight segment, the method comprises generating an associatedflight segment description that comprises one or more instances offlight intent. Each instance of flight intent provides a description ofthe aircraft's motion in at least one degree of freedom of motionthereby closing the associated degrees of freedom of motion. A flightsegment has a flight segment description that may comprise one or moreinstances of flight intent. To generate aircraft intent that willunambiguously define a trajectory, all degrees of freedom of motion mustbe closed. This may be achieved using only a single instance of flightintent if that instance affects all degrees of freedom of motion.Generally, this is not the case and a flight segment description willhave multiple instances of flight intent associated with it. Optionally,the method may also require one or more degrees of freedom of aircraftconfiguration to be closed.

The flight intent obtained may contain a complete description, that isall flight segments have all degrees of freedom of motion defined.However, in general there will be some incomplete flight segmentdescriptions requiring further instances of flight intent to closestill-open degrees of freedom of motion. Consequently, the methodfurther comprises identifying flight segments where not all degrees offreedom of motion are closed and completing the identified flightsegments by adding one or more instances of flight intent to close alldegrees of freedom of motion.

Once all flight segment descriptions are completed by adding instancesof flight intent to close all degrees of freedom of motion, the aircraftintent may be formed by collating the flight segment descriptions. Theinstances of flight intent may be expressed using a formal languagethereby reducing the complexity of collating the instance of flightintent into a description of aircraft intent expressed in a formallanguage. Where degrees of freedom of configuration are used, the methodmay further comprise identifying flight segments where not all degreesof freedom of configuration are closed and completing the identifiedflight segments by adding one or more instances of flight intent toclose all degrees of freedom of configuration, and collating the flightsegment descriptions thereby providing a description of aircraft intentfor the period of flight expressed in a formal language.

The task of adding instances of flight intent to complete the flightsegment descriptions may be assisted by using pre-defined strategies.These strategies may be stored. The strategies correspond to templatesupon which instances of flight intent may be based. A suitable strategymay be selected, and an instance of flight intent corresponding to thatstrategy may be added to the flight segment description. In order to aidselection of a suitable strategy, the strategies may be characterisedand/or identified. For example, different strategies may be formulatedto close different degrees of freedom. In this way, a class ofstrategies may be formed that relate to the vertical motion of theaircraft. This class may be further divided into groups corresponding toclimbing, descending and maintaining altitude. Different strategies mayalso apply to different phases of flight, such as take off, climb out,cruise, descent, final approach, landing and taxiing. Strategies mayalso be identified according to the phase of flight to which theyrelate. Then, a flight segment may be reviewed to determine the currentphase of flight, and an appropriate strategy selected. For example, aflight segment may apply to final approach, in which case strategies maybe selected applying to this phase of flight and that may be based ontemplates that propose decreases in altitude and decreases in speed.Strategies may also be prioritised.

The step of adding an instance of flight intent may include adding acomposite describing the flight intent, for example using a flightintent description language. The composite may correspond to acombination of flight intent descriptions, such as a combination ofdescriptions of flight intent closing more than one degree of freedom.For example, a composite may define motion aspects and alsoconfiguration aspects. In addition, the composite may define a parameterrange thereby forming a parametric aircraft intent. Parametric aircraftintent contains information to close all degrees of freedom of motion,but as ranges of parameters are specified rather than specific values,the parametric aircraft intent does not define a unique trajectory. In asense, parametric aircraft intent bridges flight intent that may notcontain information relating to all degrees of freedom and aircraftintent that closes all degree of freedom with specific parameter valuesthat allows a unique trajectory to be calculated.

The method may further comprise optimising the parametric aircraftintent by determining an optimal value for the parameter of eachparameter range. This may be done in a variety of ways, althoughevolutionary techniques such as genetic evolution offer a good choice.For example, the method may comprise generating initial parameter valuesthereby forming a model aircraft intent. These initial parameter valuesmay then be optimised, but a way of determining whether changes to theparameter values result in an improvement or not must be used. To thisend, the method may comprise defining a merit function against which theaircraft intent may be measured. That is, the method may comprisecalculating a trajectory from the model aircraft intent and calculatinga merit function value for the trajectory using the merit function. Inorder to optimise the parameter values, the method may comprise repeatediterations of amending the parameter values, calculating the resultingtrajectory and calculating the resulting merit function value. Changesin the merit function value may be used to determine whether theaircraft intent has improved.

The merit function may be based upon objectives pertaining to the periodof flight. For example, the objectives may be pre-defined by operatorsof the aircraft, such as airlines or pilots. These objectives may bestored in a user preferences model. Objectives relating to userpreferences are usually directed to safety and efficiency. Theobjectives may define functions to be optimised like: operationalrevenue such as maximising payload weight, minimising fuel consumption,minimising over-flight fees, minimising landing fees, minimisingmaintenance costs; environmental impact such as minimising COx and NOxemissions, minimising noise emissions; and quality of service such asincreasing passengers' comfort (e.g. avoiding sudden and extrememanoeuvres) and reducing delays.

In general, a description of a set of initial conditions of the aircraftat the start of the period of flight will be needed. This description ofthe initial conditions may be part of the description of flight intentobtained. Alternatively, the method may further comprise obtaining adescription of a set of initial conditions of the aircraft at the startof the period of flight and ensuring that the flight intent descriptionand the initial conditions are parsed to provide the instances of flightintent.

As noted above, the instances of flight intent may include descriptionsof aircraft configuration. The aircraft configuration may be groupedinto degrees of freedom that require definition in the aircraft intent.For example, three degrees of freedom of configuration may be required,one degree defining the configuration of the landing gear, one degreedefining the configuration of high lift devices such as flaps, and onedegree defining the configuration of the speed brakes. Landing gear maybe defined as either stowed or deployed, and the speed brakes may alsobe defined as stowed and deployed. High lift configurations may havemany more states, for example corresponding to stowed and severalextended positions.

Consequently, an aircraft may be defined by aircraft intent having sixdegrees of freedom, namely three degrees of freedom of motion, and threedegrees of freedom of configuration corresponding to landing gear, highlift devices and speed brakes.

The three degrees of freedom of motion may comprise one degreecorresponding to the lateral profile and two degrees corresponding tothe vertical profile. To close the two degrees relating to the verticalprofile, flight intent may be required that provides a description oftwo out of the following three aspects of aircraft motion: verticalpath, speed and propulsion.

The method may further comprise identifying flight segments where notall degrees of freedom of aircraft configuration are defined andcompleting the identified flight segments by adding one or moreinstances of flight intent to define all degrees of freedom of aircraftconfiguration. For example, an instance of flight intent may be addedthat defines extending the flaps during the final approach phase of aflight.

Constraints may apply to the aircraft during the flight period, forexample air traffic constraints that govern no fly zones or otherrestricted areas. Air traffic constraints may limit the trajectoryfollowed by an aircraft in one or more dimensions. They may includealtitude constraints, speed constraints, climb/descend constraints,heading/vectoring/route constraints, standard procedures constraints,route structures constraints, SID constraints, STAR constraints, andcoordination and transfer constraints (e.g. speed and altitude rangesand the location of entrance and exit points which should be respectedby any flight when it is moving from one sector to the next one).

The method may comprise checking that the aircraft intent generate asdescribed above meets one or more constraints. If any constraints arenot met, the method may comprise returning to the parsed flight intentdescription derived from the obtained flight intent. That is, alladditional information added to the flight intent originally obtained iseffectively removed and a fresh start made. Then the method may compriseidentifying flight segments where not all degrees of freedom are closedand completing the identified flight segments selecting an alternativestrategy from the plurality of stored strategies and adding an instanceof flight intent corresponding to that strategy to close all degrees offreedom. That is, the strategy used previously to augment the flightsegment description is not used in the next iteration. Then, the flightsegment descriptions are collated thereby providing an alternativedescription of aircraft intent for the period of flight expressed in aformal language. The step of checking that the aircraft intent meets oneor more constraints pertaining to the aircraft is then repeated,including a further iteration of returning to the parsed flight intentand trying further alternative strategies. Thus the method loops untilan aircraft intent satisfying all constraints is generated or until themethod otherwise terminates (e.g. self-checking suggests a validaircraft intent cannot be generated or because of a time out).

Alternatively, a more targeted approach may be made to improving theaircraft intent. For example, if checking the aircraft intent indicatesthat one or more constraints pertaining to the aircraft are not met, themethod may continue by returning to the flight description derived byparsing the obtained flight intent for the flight segments whereconstraints are not met. For these flight segments, the flight segmentmay be completed by selecting an alternative strategy from the pluralityof stored strategies and adding an instance of flight intentcorresponding to that strategy to close all degrees of freedom.

All flight segment descriptions may then be collated thereby providingan alternative description of aircraft intent for the period of flightexpressed in a formal language. The step of checking that the aircraftintent meets one or more constraints pertaining to the aircraft isrepeated as necessary, such that the method again loops until anaircraft intent is generated that meets all the constraints.

Any of the above methods may further comprise calculating a trajectoryfor the period of flight from the aircraft intent for use in a varietyof applications. For example, the trajectory may be made available to apilot for inspection. Alternatively, the aircraft may be made to fly thetrajectory either manually by a pilot or automatically by an autopilot.The aircraft intent and trajectory may be used by air traffic control.For example, air traffic control may compare trajectories found in thisway to identify conflicts between aircraft.

As will be appreciated from the above, computers and computer processorsare suitable for implementing the present disclosure. The terms“computer” and “processor” are meant in their most general forms. Forexample, the computer may correspond to a personal computer, a mainframecomputer, a network of individual computers, laptop computers, tablets,handheld computers like PDAs, or any other programmable device.Moreover, alternatives to computers and computer processors arepossible. Programmed electronic components may be used, such asprogrammable logic controllers. Thus, the present disclosure may beimplemented in hardware, software, firmware, and any combination ofthese three elements. Further, the present disclosure may be implementedin the computer infrastructure of an aircraft, or on a computer readablestorage medium having recorded thereon a computer program comprisingcomputer code instructions, when executed on a computer, cause thecomputer to perform one or more methods of the invention. All referencesabove to computer and processor should be construed accordingly, andwith a mind to the alternatives described herein.

Other aspects of the invention, along with preferred features, are setout in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the present disclosure may be more readily understood,preferred embodiments will now be described, by way of example only,with reference to the accompanying drawings in which:

FIG. 1 shows a system for computing an aircraft's trajectory usingflight intent and aircraft intent according to an embodiment of theinvention;

FIG. 2 shows the system of FIG. 1 in greater detail according to anembodiment of the invention;

FIG. 3 shows elements of the flight intent description languageaccording to an embodiment of the invention;

FIG. 4 is a diagram showing the different types of trigger conditionsaccording to an embodiment of the invention;

FIG. 5 is a method of deriving aircraft intent according to anembodiment of the invention;

FIG. 6 shows how flight intent may be completed to form parametricaircraft intent according to an embodiment of the invention;

FIG. 7 shows how parametric aircraft intent may be optimised to providea complete aircraft intent according to an embodiment of the invention;

FIG. 8 shows a lateral flight profile to be followed when approaching anairport;

FIG. 9 shows vertical flight profile restrictions that apply to theapproach shown in FIG. 8; and

FIG. 10 shows two vertical flight profiles that meet the restrictionsshown in FIG. 9.

DETAILED DESCRIPTION

A system for computing an aircraft's trajectory 100 from a descriptionof aircraft intent that is in turn derived from flight intent is shownin FIGS. 1 and 2.

FIG. 1 shows a basic structure of how flight intent 101 may be used toderive aircraft intent 114, and how aircraft intent 114 may be used toderive a description of an aircraft's trajectory 122. In essence, flightintent 101 is provided as an input to an intent generationinfrastructure 103. The intent generation infrastructure 103 determinesaircraft intent 114 using the instructions provided by the flight intent101 and other inputs to ensure a set of instructions is provided asaircraft intent 114 that will allow an unambiguous trajectory 122 to becalculated. This process may comprise intermediate steps of enrichingthe flight intent 101 and augmenting the enriched flight intent toprovide parametric aircraft intent, before finally optimising theparametric aircraft intent to produce the aircraft intent 114.

The aircraft intent 114 output by the intent generation infrastructure103 may then be used as an input to a trajectory computationinfrastructure 110. The trajectory computation infrastructure 110calculates an unambiguous trajectory 122 using the aircraft intent 114and other inputs that are required to solve the equations of motion ofthe aircraft.

FIG. 2 shows the system of FIG. 1 in further detail. As can be seen, theintent generation infrastructure 103 receives a description of theflight intent 101 as an input along with a description of the initialstate 102 of the aircraft (the initial state 102 of the aircraft may bedefined as part of the flight intent 101, in which case these two inputsare effectively one and the same). The intent generation infrastructure103 comprises an intent generation engine 104 and a pair of databases,one storing a user preferences model 105 and one storing an operationalcontext model 106.

The user preferences model 105 embodies the preferred operationalstrategies governing the aircraft and may correspond to both constraintsand objectives, e.g. the preferences of an airline with respect to loads(both payload and fuel); how to react to meteorological conditions suchas temperature, wind speeds, altitude, jet stream, thunderstorms andturbulence as this will affect the horizontal and vertical path of theaircraft as well as its speed profile; cost structure such as minimisingtime of flight or cost of flight, maintenance costs, environmentalimpact; communication capabilities; and security considerations. Theuser preferences model 105 may be used when converting the flight intentinput 101 to the aircraft intent output 114—in any of the steps ofenriching the flight intent 101, augmenting the enriched flight intentto provide parametric aircraft intent, completing the aircraft intent—byproviding further detail, as will be described in more detail below.

The operational context model 106 embodies constraints on use ofairspace. For example, the operational context model 106 may containdetails of restricted airspace and of standard terminal arrival routes(STARS) and standard instrument departures (SIDS) to be followed intoand out from an airport. The operational context model 106 is also usedwhen converting the flight intent input 101 to the aircraft intentoutput 114—in any of the steps of enriching the flight intent 101,augmenting the enriched flight intent to provide parametric aircraftintent, completing the aircraft intent—by providing further detail, aswill be described in more detail below.

The intent generation engine 104 uses the flight intent 101, initialstate 102, user preferences model 105 and operational context model 106to provide the aircraft intent 114 as its output.

FIG. 2 shows that the trajectory computation infrastructure 110comprises a trajectory engine 112. The trajectory engine 112 requires asinputs both the aircraft intent 114 described above and also the initialstate 116 of the aircraft. The initial state 116 of the aircraft may bedefined as part of the aircraft intent 114 in which case these twoinputs are effectively one and the same. For the trajectory engine 112to provide a description of the computed trajectory 122 for theaircraft, the trajectory engine 112 uses two models: an aircraftperformance model 118 and an Earth model 120.

The aircraft performance model 118 provides the values of the aircraftperformance aspects required by the trajectory engine 112 to integratethe equations of motion. These values depend on the aircraft type forwhich the trajectory is being computed, the aircraft's current motionstate (position, velocity, weight, etc) and the current localatmospheric conditions.

In addition, the performance values may depend on the intended operationof the aircraft, i.e. on the aircraft intent 114. For example, atrajectory engine 112 may use the aircraft performance model 118 toprovide a value of the instantaneous rate of descent corresponding to acertain aircraft weight, atmospheric conditions (pressure altitude andtemperature) and intended speed schedule (e.g. constant calibratedairspeed). The trajectory engine 112 will also request from the aircraftperformance model 118 the values of the applicable limitations so as toensure that the aircraft motion remains within the flight envelope. Theaircraft performance model 118 is also responsible for providing thetrajectory engine 112 with other performance-related aspects that areintrinsic to the aircraft, such as flap and landing gear deploymenttimes.

The Earth model 120 provides information relating to environmentalconditions, such as the state of the atmosphere, weather conditions,gravity and magnetic variation.

The trajectory engine 112 uses the inputs 114 and 116, the aircraftperformance model 118 and the Earth model 120 to solve a set ofequations of motion. Many different sets of equations of motion areavailable that vary in complexity, and that may reduce the aircraft'smotion to fewer degrees of freedom by means of a certain set ofsimplifying assumptions. For example, equations of motion describingaircraft motion in six degrees of freedom of motion may be used. Asimplified set of equations of motion may use only three degrees offreedom of motion.

The trajectory computation infrastructure 110 may be air-based orland-based. For example, the trajectory computation infrastructure 110may be associated with an aircraft's flight management system thatcontrols the aircraft on the basis of a predicted trajectory thatcaptures the airline operating preferences and business objectives. Theprimary role for land-based trajectory computation infrastructures 120is for air traffic management.

Using a standardised approach to describing an aircraft's trajectoryallows greater interoperability between airspace users and managers. Italso allows greater compatibility between many of the legacy softwarepackages that currently predict trajectories, even if interpreters arerequired to convert information from the standard format into aproprietary format.

Moreover, a standardised approach also works to the benefit of flightintent 101 and aircraft intent 114. For example, flight intent 101 maybe expressed using the instructions and other structures of the formallanguage implementation used to express aircraft intent 114. Inaddition, flight intent 114 provides a user with an extension to theaircraft intent language that allows flight intent 114 to be formulatedwhere only certain aspects of aircraft's motion are known. By using acommon expression format, these instances of flight intent may be easilyaugmented to form instances of aircraft intent.

As flight intent 101 may be thought of as a broader and generalised formof aircraft intent 114, it is useful to start with a consideration ofaircraft intent 114 such that key concepts also used in generatingflight intent 114 may be introduced.

Aircraft Intent

The aircraft intent description is an expression of a set ofinstructions in a formal language, an aircraft intent descriptionlanguage, which defines unambiguously the trajectory 122 of theaircraft. This expression is used by the trajectory computation engine112 to solve the equations of motion that govern the aircraft's motion.To solve the equations, the configuration of the aircraft must bespecified also. For example, configuration information may be requiredto resolve the settings of the landing gear, speed brakes and high liftdevices. Hence, the aircraft intent 114 comprises a set of instructionsincluding both configuration instructions that describe completely theaerodynamic configuration of the aircraft and motion instructions thatdescribe unambiguously how the aircraft is to be flown and hence theresulting motion of the aircraft. As the motion instructions and theconfiguration instructions are both required to define uniquely theaircraft's motion, they are together referred to herein as the definingthe degrees of freedom: motion instructions relate to the degrees offreedom of motion and configuration instructions relate to the degreesof freedom of configuration. For example, six degrees of freedom may beused to describe the aircraft such as lateral path (motion), verticalpath (motion), speed (motion), landing gear (configuration), high liftdevices (configuration) and speed brakes (configuration).

There exist in the art many different sets of equations of motion thatmay be used to describe an aircraft's motion. The sets of equationsgenerally differ due to their complexity. In principle, any of thesesets of equations may be used with the present disclosure. The actualform of the equations of motion may influence how the aircraft intentdescription language is formulated because variables that appear in theequations of motion also appear in the instructions defining theaircraft intent 114. However, the flight intent 101 is not constrainedin this way in that it may express flight intent 114 generally. Anydetail specific to the particular equations of motion to be used neednot be specified in the flight intent 101, and may be added when formingthe aircraft intent 114.

The aircraft intent description language is a formal language whoseprimitives are the instructions. The grammar of the formal languageprovides the framework that allows individual instructions to becombined into composites and then into sentences that describe flightsegments. Each flight segment contains a complete set of instructionsthat close the degrees of freedom of motion and so unambiguously definesthe aircraft trajectory 122 over its associated flight segment.

Instructions may be thought of as indivisible pieces of information thatcapture basic commands, guidance modes and control inputs at thedisposal of the pilot and/or the flight management system. Eachinstruction may be characterised by three main features: effect, meaningand execution interval. The effect is defined by a mathematicaldescription of its influence on the aircraft's motion. The meaning isgiven by its intrinsic purpose and is related to the operational purposeof the command, guidance mode or control input captured by theinstruction. The execution interval is the period during which theinstruction is affecting the aircraft's motion. The execution ofcompatible instructions may overlap, while incompatible instructionscannot have overlapping execution intervals (e.g. instructions thatcause a conflicting requirement for the aircraft to ascend and descendwould be incompatible).

Lexical rules capture all the possible ways of combining instructionsinto aircraft intent 114 such that overlapping incompatible instructionsare avoided and so that the aircraft trajectory is unambiguouslydefined.

Flight Intent

The definition of a specific aircraft trajectory is the result of acompromise between a given set of objectives to be met and a given setof constraints to be followed. These constraints and objectives areincluded as part of the flight intent 101 that could be considered as aflight blueprint. Importantly, flight intent 101 does not have todetermine the aircraft motion unambiguously: in principle, there may bemany trajectories that fulfil the set of objectives and constraintsencompassed by a given flight intent 101. An instance of flight intent101 will generally give rise to a family of aircraft intents 114, eachinstance of aircraft intent 114 resulting in a different unambiguoustrajectory. For example, flight intent may define a lateral path to befollowed but may not specify a vertical path to be followed over thesame execution interval: many aircraft intents could be generated fromthis flight intent, each aircraft intent corresponding to a differentvertical profile.

Thus, flight intent 101 must normally be supplemented with enoughinformation to allow a unique aircraft intent 114 to be determined andthus a unique trajectory. Adding to the flight intent 101 to complete anaircraft intent 114 is the responsibility of the intent generationengine 104, whereas the trajectory engine 112 assumes responsibility fordetermining the corresponding trajectory 122 from the aircraft intent114.

As explained above, each instance of flight intent 101 containstrajectory-related information that does not necessarily univocallydetermine the aircraft motion, but instead usually incorporates a set ofhigh-level conditions that define certain aspects that the aircraftshould respect during its motion (e.g. following a certain route,keeping a fixed speed in a certain area). The flight intent 101 isaugmented to capture key operational objectives and constraints thatmust be fulfilled by the trajectory (e.g. intended route, operatorpreferences, standard operational procedures, air traffic managementconstraints, etc.) by reference to the user preferences model 105 andthe operational context model 106.

Considering the information that is used directly to generate andaugment the flight intent 101, it is possible to group similar elementsinto three separate structures: flight segments, operational context anduser preferences.

The flight segments combine to form the flight path to be followed bythe aircraft during the flight, i.e. the four-dimensional trajectory ismade up of a series of successive flight segments. As explained abovewith respect to the operational context model 106, the operationalcontext may include the set of air traffic management constraints thatmay limit the trajectory followed by an aircraft in one or moredimensions. They may include altitude constraints, speed constraints,climb/descend constraints, heading/vectoring/route constraints, standardprocedures constraints, route structures constraints, SID constraints,STAR constraints, and coordination and transfer constraints (e.g. speedand altitude ranges and the location of entrance and exit points whichshould be respected by any flight when it is moving from one sector tothe next). These constraints may be retrieved from the operationalcontext model 106 and used to enrich the flight intent 101.

As explained above with respect to the user preferences model 105, userpreferences are usually directed to safety and efficiency, and generallydiffer from one user (such as an airline or pilot) to another. The mostcommon user preferences relate to: increasing operational revenue suchas maximising payload weight to be flown, minimising fuel consumption,minimising over-flight fees, minimising landing fees, and minimisingmaintenance costs; environmental impact such as minimising COx and NOxemissions, minimising noise emissions; and quality of service such asincreasing passengers' comfort (e.g. avoiding sudden and extrememanoeuvres, avoiding turbulence) and reducing delays. These preferencesmay correspond to constraints or objectives. These constraints andobjectives may be retrieved from the user preferences context model 105and used to enrich the flight intent 101.

Flight Intent Description Language (FIDL)

It is proposed to represent flight intent using a formal language,composed of a non-empty finite set of symbols or letters, known as analphabet, which are used to generate a set of strings or words. Agrammar is also required, namely a set of rules governing the allowableconcatenation of the alphabet into strings and the strings intosentences.

The alphabet comprises three types of letters, as shown in FIG. 3:flight segment descriptions, constraints and objectives. A sentence isformed by the proper combination of these elements following grammaticalrules that will be described below. A sentence is an ordered sequence offlight segment descriptions, i.e. ordered according to when they occur,in which different constraints and objectives are active to influencethe aircraft motion.

Flight segment descriptions, within the alphabet, represent the intentof changing the aircraft motion state from one state into another (e.g.a translation from one 3D point to another 3D point, a turning betweentwo courses, an acceleration between two speeds or an altitude change).A flight segment may be characterised in its flight segment descriptionby two aircraft motion states identified by a condition or event thatestablishes certain requirements for the trajectory to be flown betweenthese states. These conditions represent the execution interval of theflight segment. The conditions may close one or more degrees of freedomduring the flight segment, including both degrees of freedom of motionand of configuration.

Constraints represent restrictions on the trajectory, as describedabove, and the constraints may be achieved by making use of the opendegrees of freedom that are available during the applicable flightsegment(s).

Objectives, as described above, represent a desire relating to thetrajectory to maximize or minimize a certain functional (e.g. cruise tominimise cost). The objectives may be achieved by making use of the opendegrees of freedom that are available during the applicable flightsegment(s), excluding those that are used to respect the constraintsaffecting that flight segment(s).

Combining these three elements it is possible to build words as validFIDL strings. For example, the flight intent information “fly fromwaypoint RUSIK to waypoint FTV” can be expressed by an FIDL wordcontaining a flight segment description whose initial state is definedby the coordinates of waypoint RUSIK and whose final state is defined bythe coordinates of waypoint FTV. This flight intent description could beenriched by a constraint such as “maintain flight level above 300(FL300)”. In the same way, it would be possible to add information tothis FIDL word regarding some objectives over the trajectory such asmaximise speed. To ensure that any constraint or objective is compatiblewith a flight segment description, the affected aspect of aircraftmotion or configuration, expressed as a degree of freedom, should nothave been previously closed. In the previous example, the flight levelconstraint is compatible with the flight segment description because theflight segment description does not define any vertical behaviour. Oftenconstraints and objectives will extend over a sequence of flightsegments and so are added to multiple flight segment descriptions.

The attributes of a flight segment description are effect, executioninterval and a flight segment code. The effect provides informationabout the aircraft behaviour during the flight segment, and could rangefrom no information to a complete description of how the aircraft isflown during that flight segment. The effect is characterised by acomposite which is an aggregated element formed by groups of aircraftintent description language (AIDL) instructions or is a combination ofother composites, but need not meet the requirement for all degrees offreedom to be closed.

The execution interval defines the interval during which the flightsegment description is active, fixed by means of the begin and endtriggers. The begin and end triggers may take different forms, asindicated in FIG. 4. Explicit triggers 310 are divided into fixed 312and floating 314 triggers. Fixed triggers 312 correspond to a specifiedtime instant for starting or ending an execution interval such as to setan airspeed at a fixed time. Floating triggers 314 depend upon anaircraft state variable reaching a certain value to cause an executioninterval to start or end, such as keep airspeed below 250 knots untilaltitude exceeds 10,000 feet. Implicit triggers 320 are divided intolinked 322, auto 324 and default 326 triggers. A linked trigger 322 isspecified by reference to another flight segment, for example bystarting when triggered by the end trigger of a previous flight segment.Auto triggers delegate responsibility for determining whether theconditions have been met to the trajectory computation engine 112, forexample when conditions are not known at the intent generation time, andwill only become apparent at the trajectory computation time. Defaulttriggers represent conditions that are not known at intent generation,but are determined at trajectory computation because they rely uponreference to the aircraft performance model.

Constraints could be self-imposed by the aircraft operator such as avoidover-flight fees (in which case information relating to the constraintsare stored in the user preferences model 105), or by the operationalcontext or by air traffic management such as follow a STAR flight path(in which case information relating to the constraints are stored in theoperational context model 106). In any case, the final effect over theaircraft motion will be a limitation on the possible aircraft behaviourduring a certain interval. Constraints may be classified according tothe degree(s) of freedom affected by the constraint which is useful whendetermining whether it can be applied to a flight segment description(i.e. when determining whether that degree of freedom is open and soavailable).

Objectives are defined as a functional that can be combined into a meritfunction whose optimisation drives the process of finding the mostappropriate trajectory. The functional may define explicitly thevariable or variables used for the optimisation (e.g. altitude, climbrate, turn radius), and may return the value for them that minimises ormaximises the functional. The variables of control are related to thedegrees of freedom used to achieve the functional. Therefore, theyspecify the intention of using one or more degrees of freedom to achievethe optimisation. When no variable of control is defined, the aircraftintent generation process will use any remaining open degree of freedomto achieve the optimisation. Objectives may be classified consideringthe degree of freedom that can be affected by the objective effect.

The FIDL grammar is divided in lexical and syntactical rules. The formercontains a set of rules that governs the creation of valid words usingflight segment descriptions, constraints and objectives. The lattercontains a set of rules for the generation of valid FIDL sentences.

The lexical rules consider the flight segment descriptions as the FIDLlexemes, i.e. the minimal and indivisible element that is meaningful byitself. Constraints and objectives are considered as FIDL prefixes (orsuffixes) which complement and enhance the meaning of the lexemes but donot have any sense individually. Therefore the lexical rules describehow to combine the lexemes with the prefixes in order to ensure thegeneration of a valid FIDL string. They also determine whether a stringformed by lexemes and prefixes is valid in the FIDL.

The lexical rules are based on the open and closed degrees of freedomthat characterise a flight segment. If the flight segment has no opendegree of freedom, it means that the associated lexemes are totallymeaningful and their meaning cannot be complemented by any prefix(constraint or objective). For lexemes whose flight segments have one ormore open degrees of freedom, as many prefixes as open degrees offreedom may be added.

The FIDL syntactical rules are used to identify if a sentence formed byFIDL words is valid or not. A well-formed FIDL sentence is defined by asequence of concatenated flight segment descriptions, enriched withconstraints and objectives, that represent a chronological succession ofaircraft motion states during a period of flight.

Generation of Aircraft Intent

A method of generating aircraft intent according to an embodiment of thepresent disclosure will now be described with reference to FIG. 5.

As step 510, the intent generation infrastructure 103 is initialised tocreate a flight intent instance to be used in a specific operationalcontext, for a specific user and for a specific aircraft model.

At step 520, the flight intent 101 and initial conditions 102 arereceived by the intent generation infrastructure 103, and are parsed tocreate flight segments and corresponding flight intent objects to spaneach flight segment. Each flight object will contain a flight segmentdescription. In some embodiments, the parsed flight intent will containflight objects already augmented by constraints or objectives, forexample as already provided by an operator when defining the originalflight intent 101 as part of a mission plan or the like.

The parsed flight intent is provided to the intent generation engine 104so that it may be converted to aircraft intent 114. The intentgeneration engine 104 has at its disposal a set of strategies andheuristics to allow it to convert the flight intent 101 into aircraftintent 114 by adding information to the parsed flight intent objects toclose all degrees of freedom. This process comprises steps 530 to 560shown in summary in FIG. 5, and as shown in more detail in FIGS. 6 and7.

At step 530, the intent generation engine 104 passes the flight intentobjects to the user preferences model 105 and operational context model106 so that the flight intent 101 may be enriched. The intent generationengine 104 identifies constraints and objectives from the models 105 and106 that are relevant to each flight intent object (e.g. not all theconstraints included in the operational context are likely to apply to aspecific route or to all flight segments on a particular flight path).How relevant constraints and objectives are identified is described inmore detail below. The intent generation engine 104 enriches the flightintent 101 by expanding the flight intent objects to add the relevantconstraints and objectives to the associated flight segment descriptionsaccording to the syntactical and lexical rules imposed by the flightintent description language. The output of step 530 is an enrichedflight intent.

At step 540, the intent generation engine 104 identifies flight intentobjects of the enriched flight intent having open degrees of freedom.The intent generation engine 104 fills these flight intent objects withcomposites to close all degrees of freedom. This process is driven byseveral completion strategies based on the sequence and type of anyconstraints included in the enriched flight intent object. In general,constraints will not cause a particular parameter to be uniquelyspecified, but instead usually set a range of parameters. For example, aconstraint added to a flight intent object may specify a maximumairspeed to be flown leaving open a range of airspeed parameters.

As step 550, the intent generation engine 104 optimises the parametricaircraft intent. This optimisation process takes all the parameterranges specified in the parametric aircraft intent, and calculatesoptimal values for each parameter by optimising an overall meritfunction that is calculated from all the objectives present in theenriched flight intent. The parametric ranges specified in each flightintent object are then replaced by the optimal values.

At the end of the optimisation step 550, the method proceeds to step 560where the intent generation engine 104 checks that the predictedtrajectory for the aircraft intent fulfils all constraints defined bythe operational context model 106, user preferences model 105 and theflight intent 101.

If all constraints are fulfilled, the method ends at step 570 wherecompleted aircraft intent 114 is provided and/or a description of thecorresponding trajectory 122 is provided. If any constraints are foundnot to be fulfilled, the method returns to step 540 where the originalset of enriched flight intent provided at step 530 is retrieved and theintent generation engine 104 uses an alternative strategy to completethe flight intent by inserting composites. The method then continues asbefore through steps 540, 550 and 560. A number of iterations of theloop may be performed in an attempt to find a solution. For example,strategies may be ranked such that the intent generation engine 104selects strategies in turn according to rank until an aircraft intent114 is formed that is found to meet all constraints at step 560.Self-checking is performed such that the intent generation engine 104will return an exception declaring the impossibility of generating anaircraft intent based on the initial flight intent 101 in the definedoperational context. The declaration of an exception may be triggeredafter a set number of iterations or after a pre-defined time delay.

Flight Intent Enrichment

At step 530 in FIG. 5, the intent generation engine 104 enriches theflight intent objects with constraints and objectives retrieved from theuser preferences model 105 and/or the operational context model 106. Todo this, the intent generation engine 104 identifies constraints andobjectives from the models 105 and 106 that are relevant to each flightintent object (e.g. not all the constraints included in the operationalcontext are likely to apply to a specific route or to all flightsegments on a particular flight path).

Relevance of constraints and objectives to flight intent objects may bedetermined using descriptions associated with the data stored in theuser preferences model 105 and the operational context model 106. Forexample, data may be identified by the geographical region to which itapplies and/or by the phase of flight to which it applies. For example,the operational context model 106 may contain a topographicaldescription of several regions within an airspace. Each region may havea description of hazards to be avoided such as mountains and denselypopulated areas. A flight intent object that will apply within thatregion may be augmented with the associated constraints for that region.As a further example, the operational context model 106 may containdescriptions of STARs to be followed when arriving at an airport. Theflight intent 101 may indicate a preferred arrival waypoint into theterminal area, and so only the STAR description relating to that arrivalpoint would be relevant, and so its constraints may be added to theflight intent objects of the corresponding flight segments.

Turning to the user preferences model 105, this may contain an airline'spreferences relating to different phases of flight or to differentaircraft types. For example, it might define that during take off andclimb out, the aircraft is flown to minimise fuel consumption.Alternatively, the user preferences model 105 might define that duringdescent, the aircraft is maintained at the maximum altitude possible foras long as possible. It will be appreciated that flight segmentsrelating to the descent phase of a flight may then have an associatedobjective to maintain maximum altitude.

The intent generation engine 104 enriches the flight intent 101 byexpanding the flight intent objects to add relevant constraints andobjectives to the associated flight segment descriptions according tothe syntactical and lexical rules imposed by the flight intentdescription language. The output of step 530 is an enriched flightintent that has flight intent objects comprising flight segmentdescriptions that may or may not be enriched with constraints andobjectives.

Generating a Parametric Aircraft Intent

At step 540, the intent generation engine 104 closes any open degrees offreedom within flight intent objects. Thus, the enriched flight intentthat may still contain open degrees of freedom is completed to ensureall degrees of freedom of motion and configuration are closed for allflight intent objects. At this stage, parametric ranges may be used toclose degrees of freedom, such that parametric aircraft intent isformed. This contains information on all degrees of freedom, but doesnot contain specific values for parameters such that the parametricaircraft intent does not define a unique trajectory.

FIG. 6 shows how the enriched flight intent may be completed to form aparametric aircraft intent. The process starts at 610 where the firstflight segment is selected. The flight segments may be ordered in anyway, although ordering the flight segments chronologically is theobvious example. The ordering merely needs to provide a list of flightsegments that may be processed sequentially.

After the first flight segment has been selected at 610, the processcontinues to a routine indicated at 620 in FIG. 6. The routine 620 isrepeated for each flight segment in turn, as will be now be described.

At step 630, the selected flight segment is checked to see whether ithas any open degrees of freedom. If not, the method continues to step615 where the next flight segment is selected and the process entersroutine 620 once more. If one or more open degrees of freedom are foundat step 630, that flight segment continues through procedure 620 forfurther processing.

Next, at step 640, the flight segment description and any constraintspertaining to the current flight segment are retrieved. This data isused at step 650 to select an appropriate strategy for completing theopen degrees of freedom. This may be done by looking at which degree ordegrees of freedom must be closed. For example, the open degrees mayrelate to the vertical flight profile or may relate to landing gearconfiguration. The intent generation engine 104 has at its disposalstrategies corresponding to templates for closing particular degrees offreedom. These strategies are tagged to identify to which degrees offreedom they relate. Composites may also be stored and associated with astrategy, ready for selection by the intent generation engine 104 andinsertion into the flight segment description.

The following are examples of strategies and associates composites:geometric paths providing different lateral path composites to definedifferent path shapes (e.g. right turn, left turn, sequence of turns),level flight, constant path angle ascend/descend, constant speedascend/descend, general ascend/descend, CAS-MACH climb, MACH-CASdescend, level trust acceleration/deceleration, clean configuration(e.g. of landing gear, high lift devices and speed brakes), andscheduled configuration settings (e.g. landing gear deployed and highlift device extension for landing).

The strategies may also be tagged to indicate to which phase of flightthey apply (e.g. take off, climb out, cruise, descent, final approach,landing, taxiing). The constraints are also used in determining whichstrategy should be selected. Returning to the example above, aconstraint may specify a region of restricted airspace that is nearby,thus guiding the strategy chosen to ensure that the turn is made at anappropriate point to avoid the restricted airspace.

Heuristics may also be used when selecting a strategy. For example, aflight segment may not close the vertical profile. The intent generationengine 104 may revert back to the earlier flight segments to find thelast altitude specified and may then scan ahead to find the next flightsegment that specifies an altitude. Comparison of the two altitudes maythen guide selection of a suitable strategy. For example, if two flightsegments specify the same altitude, intervening flight segments that donot specify an altitude may be amended using a strategy that maintainslevel flight.

Once a suitable strategy has been selected at step 650, the procedure620 continues to step 660 where an aircraft intent primitivecorresponding to the selected strategy is generated and added to theflight segment description of the flight intent object being processed.The primitive may be added as part of a composite where two or moreprimitives are to be combined, i.e. a strategy may require a primitiveor a composite of primitives to describe the required instructionsdepending upon the complexity of the strategy.

Steps 650 and 660 are performed as necessary to ensure all open degreesof freedom are closed. With this processing finished, at step 670 acheck is made to see whether the flight segment being processed is thefinal flight segment. If not, the process loops back to step 615 wherethe next flight segment is selected and procedure 620 is entered oncemore.

When all flight segments have been processed, as determined at step 670,the process continues to step 680 where all the completed flight objectsare collated to form the parametric aircraft intent, expressed using aformal language (the aircraft intent description language). Thiscompletes step 540 of FIG. 5. The parametric aircraft intent is thenprocessed according to step 550 where the parametric ranges are resolvedinto specific parameter values through an optimisation process that willnow be described with respect to FIG. 7.

Optimising the Parametric Aircraft Intent

The optimisation process of step 550 takes all the parameter rangesspecified in the parametric aircraft intent and calculates optimalvalues for each parameter by optimising an overall merit function thatreflects the objectives defined in the flight intent objects.

As shown in FIG. 7, the process starts at step 710 where the firstflight segment is selected. As described above, the flight segments maybe ordered in any way that provides a list of flight segments forprocessing sequentially.

At step 720, the fight segment is reviewed to determine whether itcontains any parameter ranges than need resolving. If not, the methodproceeds to step 725 where the next flight segment is selected forprocessing. When a flight segment is found at step 710 to define one ormore parameter ranges, that parameter range and any associatedobjectives are retrieved and stored in respective lists, as shown atstep 730. Then, at step 740, a check is made to see if the flightsegment being processed currently is the final flight segment. If not,the process loops back to step 725 so that the next flight segment maybe selected for processing at step 720 once more. In this way, allflight segments are checked for parameter ranges, and lists are compiledthat collate the parameter ranges to be resolved along with associatedobjectives.

At step 750, the objectives stored in the associated list aremathematically combined into a merit function that reflects all theobjectives. The objectives may be stored in the user preferences model105 as a mathematical function expressing the objective to be targeted.Then, forming the merit function may correspond to combining theindividual mathematical functions describing each objective. Themathematical functions may be combined in any straightforward manner.For example, a weighted combination may be formed, where weights areassigned to each objective according to its importance. Data may bestored in the user preferences model 105 to indicate the relativeimportance of the objectives.

If a parameter range is found that does not have an associatedobjective, a library of pre-defined mathematical functions may be usedto provide a mathematical function for inclusion in the merit function.For example, a mathematical function may be associated with theparameter range that assigns a constant value irrespective of theparameter value chosen, such that the parameter value may be chosen asany within the parameter range, but optimised to lead to an overallimprovement of the merit function value. For example, selection of aparticular value for the parameter may contribute to achieving anobjective relating to the preceding flight segment.

Consequently, the merit function rewards how well the objectives are metand penalises how badly the objectives are not met.

At step 760, each parameter range in the associated list is read, andthe associated flight intent object that appears in the parametricaircraft intent is amended such that the parameter range is replaced bya value falling within the range. Different schemes may be used toselect a value, for example by selecting the maximum value, the minimumvalue, the mean value or by randomly generating a value. At the end ofstep 760, an aircraft intent results that has all parameters defined andwith no parameter ranges remaining. This model aircraft intent is thentested by using the trajectory engine 112 to calculate the correspondingtrajectory, from which the intent generation engine 104 can calculatethe merit function value for the model aircraft intent.

The process then proceeds to step 780 where the model aircraft intent isoptimised. This optimisation process improves the parameter valuesiteratively. That is, intent generation engine 104 goes throughiterations of randomly changing some or all the parameter values, thencalling the trajectory engine 112 to compute the new trajectory, andcomputing the new merit function value and determining whether it hasbeen improved. In this way, the parameter values are evolved in a waythat optimises the merit function. This may be done using any well knowntechnique, such as using evolutionary algorithms like genetic algorithmsor through linear optimisation. These techniques provide an optimisedcomplete aircraft intent, and this is provided as an output at step 790.

Example of Approach to Airport

An example of the above methods will now be described with reference toFIGS. 8 to 10. In this example, an aircraft 810 is approaching anairport to land on a runway 820. The flight intent may merely specifythat the aircraft is to land on runway 820 after arrival at waypointALPHA.

In order to provide a complete aircraft intent, the intent generationengine 104 may augment this basic flight intent with informationretrieved from the operational context model 106 describing a STARprocedure to be followed when approaching the airport. For example,intent generation engine 104 may establish the wind direction, determinethe direction for a headwind approach to the runway 820, and retrievethe STAR procedure for such a landing for aircraft arriving at waypointALPHA.

The STAR procedure will correspond to a set of restrictions. In thisexample, the lateral path to be followed routes the aircraft throughwaypoints ALPHA, BETA, GAMMA and DELTA, ready for a final straightapproach to runway 820. These waypoints are shown in FIG. 9. The STARprocedure may also contain restrictions on speeds along the route aswell as altitudes to be maintained at each waypoint. These altitudes areshown in FIG. 10.

At waypoint ALPHA, a broad permissible altitude range is defined, asindicated at 910. Smaller altitude ranges are defined for waypoints BETAand GAMMA, as shown at 920 and 930 respectively. A specific altitude isdefined for waypoint DELTA as shown at 940, corresponding to a startingaltitude for final approach from which a glide slope may be intercepted.

The intent generation engine 104 may use these restrictions to augmentthe flight intent. For example, additional flight segments may becreated corresponding to the segments between the waypoints to befollowed. Moreover, parametric intent may be created where the altituderanges at each waypoint are defined without a specific altitude beingprovided. Objectives may be used to specify altitudes to be met, asfollows.

FIG. 10 shows two alternative vertical profiles, 810 a and 810 b.Profile 810 a corresponds to aircraft 810 being operated by an airlinethat prefers to fly as high as possible for as long as possible. Thisobjective will be recorded in the user preferences model 105.Accordingly, the intent generation engine 104 sets altitudes at eachwaypoint as the maximum specified, then calculates the maximum rate ofdescent possible for the aircraft 810 to establish when each descentphase must begin, and creates segments that define level flight betweeneach descent phase, along with defining the top of descent point (TOD2).Thus, by using the objective, intent generation engine 104 generatesaircraft intent that will produce the stepped-down vertical profileshown at 810 a. This profile sees the aircraft 810 fly as high aspossible for as long as possible before making a steep descent just intime to meet the maximum altitude prescribed for each waypoint.

Another airline may not like such an approach that sees the aircraftaccelerate between level flight and descents a number of times. Thissecond airline may prefer to fly a steady continuous descent withminimal changes in flight path angle. This approach may be reflected asan objective stored in the user preferences model 105. Intent generationengine 104 may retrieve this objective, and determine the verticalprofile shown as 810 b in FIG. 10. This vertical profile sees a steadydescent with constant flight path angle from a calculated top of descentpoint TOD1 that passes through all the required altitude ranges.

As can be seen from FIG. 10, some variation in flight path angle may bemade while still ensuring the altitude restrictions are met. Furtherobjectives may guide the final selection of vertical profile. Forexample, the airline may have a further objective of flying continuousdescent approaches with the throttles set to idle and with minimaldeployment of speed brakes. This objective may then be used by theintent generation engine 104 to set an appropriate flight path angle.

Objectives to fly a constant flight path angle during descent and to flycontinuous descent approaches at idle complement each other in that theyboth affect the vertical profile. At times, these objectives will causea conflict in that both cannot be met. To avoid this, objectives may beprioritised such that the intent generation engine 104 can determinewhich objective is to be met where conflicts arise.

The airline may store restrictions in the user preferences model 105 aswell as objectives. For example, as explained above, the lateral profileis defined in part by the waypoints specified in the STAR description inthe operational context model 106. However, these restrictions leaveopen how the aircraft 810 makes the turns to meet the lateral positionof each of waypoints ALPHA, BETA, GAMMA and DELTA. The airline may alsoset restrictions, for example not to exceed a certain bank angle for thebenefit of passenger comfort. The intent generation engine 104 mayretrieve this objective from the user preferences model 105 during theflight intent enrichment step 530. At step 550, this restriction may beused to set a parameter range for the bank angle which is then optimisedat step 560.

Contemplated Applications

The present disclosure may find utility on any application that requiresprediction of an aircraft's trajectory. For example, the trajectorycomputation infrastructure 110 may be provided as part of a flightmanagement system of an aircraft. The flight management system may makeuse of the trajectory prediction facility when determining how theaircraft is to be flown.

A trajectory predicted as described in the preceding paragraph may beprovided to air traffic management, akin to the provision of a detailedflight plan.

For an air-based trajectory computation infrastructure, the flightmanagement system may have access to some of the information required togenerate the aircraft intent. For example, airline preferences may bestored locally for retrieval and use. Moreover, the aircraft performancemodel 118 and Earth model 120 may be stored locally and updated asnecessary. Further information may be input by the pilot, for examplethe particular SID, navigation route and STAR to be followed, as well asother preferences like when to deploy landing gear, change flapsettings, engine ratings, etc. Some missing information may be assumed,e.g. flap and landing gear deployment times based on recommendedairspeed.

All this required information may be acquired before a flight, such thatthe trajectory of the whole flight may be predicted. Alternatively, onlysome of the information may be acquired before the flight and the restof the information may be acquired en route. This information may beacquired (or updated, if necessary) following a pilot input, for examplein response to a change in engine rating or flight level. The trajectorycomputation infrastructure 110 may also update the predicted trajectory,and hence the aircraft intent as expressed in the aircraft intentdescription language, due to changes in the prevailing atmosphericconditions, as updated through the Earth model 120. Updates may becommunicated via any of the types of well-known communication link 230between the aircraft and the ground: the latest atmospheric conditionsmay be sent to the aircraft and the revised aircraft intent or predictedtrajectory may be sent from the aircraft.

Air traffic management applications will be similar to the abovedescribed air-based system. Air traffic management may have informationnecessary to determine aircraft intent, such as flight procedures (SIDs,STARs, etc), information relating to aircraft performance (as anaircraft performance model), atmospheric conditions (as an Earth model),and possibly even airline preferences. Some information, such as pilotpreferences relating to for example when to change the aircraftconfiguration, may be collected in advance of a flight or during aflight. Where information is not available, air traffic management maymake assumptions in order for the aircraft intent to be generated andthe trajectory to be predicted. For example, an assumption may be madethat all pilots will deploy their landing gear ten nautical miles from arunway threshold or at a particular airspeed.

Air traffic management may use the predicted trajectories of aircraft toidentify potential conflicts. Any potential conflicts may be resolved byadvising one or more of the aircraft of necessary changes to theirflight/aircraft intent.

The person skilled in the art will appreciate that variations may bemade to the above described embodiments without departing from the scopeof the invention defined by the appended claims.

The invention claimed is:
 1. A computer-implemented method of generatinga description of aircraft intent expressed in a formal language thatprovides an unambiguous description of an aircraft's intended motion andconfiguration during a period of flight, comprising: obtaining adescription of flight intent corresponding to a flight plan spanning theperiod of flight; ensuring that the flight intent description is parsedto provide instances of flight intent, each instance of flight intentspanning a flight segment with a plurality of flight segments togetherspanning the period of flight, wherein the plurality of flight segmentsrepresent an intent of changing an aircraft motion state from one stateinto another; for each flight segment, following a set of attributescomprising an effect, an execution interval, and a flight segment codethat govern a creation of valid words, wherein the effect comprisesaircraft behavior exhibited during the flight segment represented by acomposite, the execution interval defines an interval during which theflight segment is active defining an initial aircraft state and a finalaircraft state, and the flight segment code comprises an alphanumericstring indicating degrees of freedom of motion of the aircraft that arenot closed by the composite; for each flight segment, generating anassociated flight segment description that comprises at least one ormore instances of flight intent, wherein each instance of the at leastone or more instances of flight intent provides a description of theaircraft's motion in at least one degree of freedom of motion therebyclosing the at least one degree of freedom of motion and/or provides adescription of the aircraft's configuration to close at least one degreeof freedom of configuration; identifying the plurality of flightsegments where not all degrees of freedom are closed and completing theidentified flight segments by adding one or more instances of flightintent to close all degrees of freedom; and collating flight segmentdescriptions thereby providing the description of aircraft intent forthe period of flight expressed in the formal language to assist inflying the aircraft with the unambiguous description of the aircraft'sintended motion and configuration during the period of flight.
 2. Themethod of claim 1, wherein adding one or more instances of flight intentcomprises selecting a strategy from a plurality of stored strategies andadding an instance of flight intent corresponding to the strategy. 3.The method of claim 2, wherein the plurality of stored strategies areidentified by the degrees of freedom the plurality of stored strategiesinfluence, and a strategy is selected to close a degree of freedom fromthe plurality of stored strategies identified to influence the degree offreedom.
 4. The method of claim 2, wherein the plurality of storedstrategies are identified by a phase of flight to which the plurality ofstored strategies apply, and a strategy is selected to close a degree offreedom from the strategies identified to influence the degree offreedom and identified to apply to the phase of flight associated withthe flight segment.
 5. The method of claim 2 wherein the step of addingan instance of flight intent includes providing a parameter rangethereby forming a parametric aircraft intent, and the method furthercomprises optimizing the parametric aircraft intent by determining anoptimal value for a parameter of the parameter range.
 6. The method ofclaim 5, wherein determining the optimal values comprises: generatinginitial parameter values thereby forming a model aircraft intent;calculating a trajectory from the model aircraft intent; calculating amerit function value for the trajectory using a merit function; andrepeated iterations of amending the initial parameter values,calculating a resulting trajectory and calculating a resulting meritfunction value to determine whether the description of aircraft intentis improved, thereby optimizing the initial parameter values byimproving the merit function value.
 7. The method of claim 6, comprisingretrieving objectives pertaining to the period of flight and using theobjectives to form the merit function; and wherein the objectives arepre-defined by operators of the aircraft and are stored in a userpreferences model, the objectives representing a desire relating to atrajectory to maximize or minimize a function.
 8. The method of claim 7,further comprising for each objective following the set of attributescomprising the effect, a domain of application, and the executioninterval, wherein the effect comprises a mathematical expression whichdefines an influence of the objective in the motion of the aircraft, thedomain of the application comprises the interval where the objective isactive and in which the effect is applied to the motion of the aircraft,and the execution interval indicates when the objective is consideredactive in a trajectory prediction process.
 9. The method of claim 1wherein the description of flight intent obtained includes a descriptionof a set of initial conditions of the aircraft at a start of the periodof flight.
 10. The method of claim 1 further comprising obtaining adescription of a set of initial conditions of the aircraft at a start ofthe period of flight and ensuring that the flight intent description andthe initial conditions are parsed to provide the instances of flightintent.
 11. The method of claim 1 further comprising: checking that theaircraft intent meets one or more constraints, representing arestriction on a trajectory of the aircraft, and when the aircraftintent does not meet one or more constraints pertaining to the aircraft:returning to the parsed flight intent description derived from theobtained flight intent; identifying flight segments where not alldegrees of freedom are closed and completing the identified flightsegments selecting an alternative strategy from the plurality of storedstrategies and adding an instance of flight intent corresponding to thealternative strategy to close all degrees of freedom; collating theflight segment descriptions thereby providing an alternative descriptionof aircraft intent for the period of flight expressed in the formallanguage; and repeating the step of checking that the aircraft intentmeets one or more constraints pertaining to the aircraft.
 12. The methodof claim 11, wherein the following the set of attributes furthercomprises for the one or more constraint following the set of attributescomprising the effect, a domain of application, and the executioninterval, wherein the effect comprises a mathematical expression whichdefines an influence of the constraint on the motion of the aircraft,the domain of the application comprises an interval where the constraintis active and in which the effect is applied to the motion of theaircraft, and the execution interval indicates when the constraint isconsidered active in a trajectory prediction process.
 13. The method ofclaim 1 further comprising: checking that the aircraft intent meets oneor more constraints, representing a restriction on a trajectory of theaircraft, and when the aircraft intent does not meet one or moreconstraints pertaining to the aircraft: for the flight segments wherethe one or more constraints are not met, returning to the flightdescription derived by parsing the obtained flight intent, completingthe flight segment by selecting an alternative strategy from theplurality of stored strategies and adding an instance of flight intentcorresponding to the alternative strategy to close all degrees offreedom; collating the flight segment descriptions thereby providing analternative description of aircraft intent for the period of flightexpressed in the formal language; and repeating the step of checkingthat the aircraft intent meets one or more constraints pertaining to theaircraft.
 14. The method of claim 13, wherein the following the set ofattributes further comprises for the one or more constraint followingthe set of attributes comprising the effect, a domain of application,and the execution interval, wherein the effect comprises a mathematicalexpression which defines an influence of the constraint on the motion ofthe aircraft, the domain of the application comprises an interval wherethe constraint is active and in which the effect is applied to themotion of the aircraft, and the execution interval indicates when theconstraint is considered active in a trajectory prediction process. 15.The method of claim 1 comprising calculating a trajectory for the periodof flight from the aircraft intent and, optionally, causing the aircraftto fly the trajectory or comparing the trajectory with trajectories ofother aircraft to identify conflicts.
 16. A system for generating adescription of aircraft intent expressed in a formal language thatprovides an unambiguous description of an aircraft's intended motion andconfiguration during a period of flight, the system comprising: aprocessor; a storage medium comprising instructions thereon, that whenexecuted by said processor, cause the processor to: obtain a descriptionof flight intent corresponding to a flight plan spanning a period offlight; ensure that the flight intent description is parsed to provideinstances of flight intent, each instance of flight intent spanning aflight segment with a plurality of flight segments together spanning theperiod of flight, wherein the plurality of flight segments represent anintent of changing an aircraft motion state from one state into another;for each flight segment, follow a set of attributes comprising aneffect, an execution interval, and a flight segment code that govern acreation of valid words, wherein the effect comprises aircraft behaviorexhibited during the flight segment represented by a composite, theexecution interval defines an interval during which the flight segmentis active defining an initial aircraft state and a final aircraft state,and the flight segment code comprises an alphanumeric string indicatingdegrees of freedom of motion of the aircraft that are not closed by thecomposite; for each flight segment, generate an associated flightsegment description that comprises at least one or more instances offlight intent, wherein each instance of the at least one or moreinstances of flight intent provides a description of the aircraft'smotion in at least one degree of freedom of motion thereby closing theat least one degree of freedom of motion and/or provides a descriptionof the aircraft's configuration to close at least one degree of freedomof configuration; identify flight segments where not all degrees offreedom are closed and complete the identified flight segments by addingone or more instances of flight intent to close all degrees of freedom;and collate flight segment descriptions thereby providing thedescription of aircraft intent for the period of flight expressed in theformal language to assist in flying the aircraft with the unambiguousdescription of the aircraft's intended motion and configuration duringthe period of flight.
 17. The system of claim 16 wherein adding one ormore instances of flight intent comprises selecting a strategy from aplurality of stored strategies and adding an instance of flight intentcorresponding to the strategy.
 18. The system of claim 17 wherein theplurality of stored strategies are identified by the degrees of freedomthe plurality of stored strategies influence, and a strategy is selectedto close a degree of freedom from the plurality of stored strategiesidentified to influence the degree of freedom.
 19. The system of claim17 wherein the plurality of stored strategies are identified by a phaseof flight to which the plurality of stored strategies apply, and astrategy is selected to close a degree of freedom from the plurality ofstored strategies identified to influence the degree of freedom andidentified to apply to the phase of flight associated with the flightsegment.
 20. The system of claim 17 wherein the step of adding aninstance of flight intent includes providing a parameter range therebyforming a parametric aircraft intent, and the system further comprisesinstructions, that when executed by the processor, cause the processorto optimize the parametric aircraft intent by determining an optimalvalue for a parameter of the parameter range.
 21. The system of claim20, wherein determining the optimal values comprises: generating initialparameter values thereby forming a model aircraft intent; calculating atrajectory from the model aircraft intent; calculating a merit functionvalue for the trajectory using a merit function; and repeated iterationsof amending the initial parameter values, calculating a resultingtrajectory and calculating a resulting merit function value to determinewhether the description of aircraft intent is improved, therebyoptimizing the initial parameter values by improving the merit functionvalue.
 22. An aircraft comprising: a processor; a storage mediumcomprising instructions thereon, that when executed by said processor,cause the processor to: obtain a description of flight intentcorresponding to a flight plan spanning a period of flight; ensure thatthe flight intent description is parsed to provide instances of flightintent, each instance of flight intent spanning a flight segment with aplurality of flight segments together spanning the period of flight,wherein the plurality of flight segments represent an intent of changingan aircraft motion state from one state into another; for each flightsegment, follow a set of attributes comprising an effect, an executioninterval, and a flight segment code that govern a creation of validwords, wherein the effect comprises aircraft behavior exhibited duringthe flight segment represented by a composite, the execution intervaldefines an interval during which the flight segment is active definingan initial aircraft state and a final aircraft state, and the flightsegment code comprises an alphanumeric string indicating degrees offreedom of motion of the aircraft that are not closed by the composite;for each flight segment, generate an associated flight segmentdescription that comprises at least one or more instances of flightintent, wherein each instance of the at least one or more instances offlight intent provides a description of the aircraft's motion in atleast one degree of freedom of motion thereby closing the at least onedegree of freedom of motion and/or provides a description of theaircraft's configuration to close at least one degree of freedom ofconfiguration; identify flight segments where not all degrees of freedomare closed and complete the identified flight segments by adding one ormore instances of flight intent to close all degrees of freedom; andcollate flight segment descriptions thereby providing the description ofaircraft intent for the period of flight expressed in a formal languageto assist in flying the aircraft with an unambiguous description of theaircraft's intended motion and configuration during the period offlight.
 23. A tangible computer readable storage medium having recordedthereon instructions that, when executed on a computer, cause thecomputer to: obtain a description of flight intent corresponding to aflight plan spanning a period of flight; ensure that the flight intentdescription is parsed to provide instances of flight intent, eachinstance of flight intent spanning a flight segment with a plurality offlight segments together spanning the period of flight, wherein theplurality of flight segments represent an intent of changing an aircraftmotion state from one state into another; for each flight segment,follow a set of attributes comprising an effect, an execution interval,and a flight segment code that govern a creation of valid words, whereinthe effect comprises aircraft behavior exhibited during the flightsegment represented by a composite, the execution interval defines aninterval during which the flight segment is active defining an initialaircraft state and a final aircraft state, and the flight segment codecomprises an alphanumeric string indicating degrees of freedom of motionof the aircraft that are not closed by the composite; for each flightsegment, generate an associated flight segment description thatcomprises at least one or more instances of flight intent, wherein eachinstance of the at least one or more instances of flight intent providesa description of the aircraft's motion in at least one degree of freedomof motion thereby closing the at least one degree of freedom of motionand/or provides a description of the aircraft's configuration to closeat least one degree of freedom of configuration; identify flightsegments where not all degrees of freedom are closed and complete theidentified flight segments by adding one or more instances of flightintent to close all degrees of freedom; and collate flight segmentdescriptions thereby providing the description of aircraft intent forthe period of flight expressed in a formal language to assist in flyingthe aircraft with an unambiguous description of the aircraft's intendedmotion and configuration during the period of flight.